Patient Health Resource: Colorectal Cancer

Colorectal cancer is cancer that occurs in the colon or rectum. It usually begins as an abnormal growth called a polyp. Regular screening can help identify colorectal cancer early when treatment is more likely to be effective.


To understand colorectal cancer, it helps to understand the colon and rectum. The large intestine (colon) is a long, tube-like, organ connected to the small intestine at one end and to the anus at the other end. It has four parts: the cecum, colon, rectum and anal canal. Partly digested food moves through the large intestine where nutrients and electrolytes are removed before the remainder is evacuated. Different types of polyps can form in the large intestine and, over time, may become cancerous. Screening can help identify if you have polyps and what types. Based on the results, your primary care physician (PCP) can determine how frequently you should be screened for colorectal cancer.

A colonoscopy is an examination of the inside of your large intestine using an endoscope, which is a thin tube containing a camera inside. It helps physicians diagnose gastrointestinal diseases, including colon cancer. It may also be used to help treat and prevent colorectal cancer. Healthcare providers recommend routine colonoscopies for middle-aged and older adults to screen for cancer. Alternative, at-home screening options for colon cancer are also available. Discuss with your physician which option is best for you.

Colorectal cancer might not cause symptoms right away but changes in bowel habits are often one of the first signs. Colorectal cancers may cause bleeding in the digestive tract which presents as blood in the stool. Over time, this internal bleeding can contribute to low red blood cell count (anemia). Sometimes colorectal cancer is suspected due to a blood test showing a low red blood cell count. These symptoms also may be caused by conditions other than colorectal cancer which is why screening is important. Additional signs and symptoms are identified below.


The risk of getting colorectal cancer increases as you get older. Other risk factors include:

  • Inflammatory bowel disease such as Crohn’s disease or ulcerative colitis
  • A family history of colorectal cancer or colorectal polyps
  • A genetic syndrome such as familial adenomatous polyposis (FAP) or hereditary non-polyposis colorectal cancer (Lynch syndrome)

Lifestyle factors that may contribute to an increased risk of colorectal cancer include:

  • Lack of regular physical activity
  • A diet low in fruit and vegetables
  • A low-fiber and high-fat diet, or a diet high in processed meats
  • Being overweight
  • Alcohol consumption
  • Tobacco use


According to the Centers for Disease Control and Prevention (CDC), the most effective way to reduce your risk of colorectal cancer is to receive routine screening. Adults ages 45 to 75 should be screened for colorectal cancer. The decision to be screened between ages 76 and 85 should be made on an individual basis. If you are older than 75, talk to your doctor about screening. People at an increased risk of getting colorectal cancer should talk to their doctor about when to begin screening, which test is right for them and how often to get tested.

These are additional steps that can help prevent colon cancer:

  • Consuming a diet low in animal fats and high in fruit, vegetables and whole grains may help reduce the risk of multiple chronic diseases, including colorectal cancer. Research is ongoing to determine the link between diet and cancer risk.
  • Studies suggest that regular physical activity, maintaining a healthy wait, along with limiting or avoiding alcohol consumption may reduce the risk of developing colorectal cancer.
  • If you smoke, quit.
    • The CDC offers free support to help you quit smoking, including coaching sessions, a customized “quit plan,” educational materials, plus referrals to local resources. Call 1-800-QUIT-NOW (1-800-784-8669).


Colorectal polyps, abnormal growths in the colon or rectum, can turn into cancer if not removed. In its early stages, colorectal cancer may not cause any detectible symptoms which is why regular screening for colorectal cancer is important.

Once symptoms appear, they may include:

  • A change in bowel habits which may include any of the following:
    • Diarrhea
    • Constipation
    • Change in stool consistency
    • Dark brown or black stools or bright, red blood on your stool
    • A feeling that the bowel is not fully emptying
  • Anemia which can cause shortness of breath or fatigue
  • Abdominal pain – persistent aches, cramps or gas
  • Unexplained weight loss 

If you experience any of these symptoms, discuss them with your primary care physician.


A colonoscopy is the preferred test for evaluating symptoms suggestive of colon cancer.  However, prior to onset of symptoms, there are several screening tests that can lead to early detection of colon cancer.  Early detection is related to higher likelihood of curing colon cancer. 

Stool tests

  • The guaiac-based fecal occult blood test (gFOBT) uses the chemical guaiac to detect blood in the stool. This test is performed once a year. For this test, you receive a test kit from your health care provider. At home, you use a stick or brush to obtain a small amount of stool. You return the test kit to the doctor or a lab, where the stool samples are checked for the presence of blood.
  • The fecal immunochemical test (FIT) uses antibodies to detect blood in the stool. This test is also performed once a year in the same way as a gFOBT.
  • The FIT-DNA test (also referred to as the stool DNA test) combines the FIT with a test that detects altered DNA in the stool. For this test, you collect an entire bowel movement and send it to a lab, where it is checked for altered DNA and for the presence of blood. This test is performed once every three years.

Flexible Sigmoidoscopy

For this test, the doctor inserts a thin, flexible, lighted tube into your rectum. The doctor checks for polyps or cancer inside the rectum and lower third of the colon. This examination is recommended every five years, or every 10 years with a FIT every year.


This procedure is similar to flexible sigmoidoscopy, except the doctor uses a longer, lighted tube to check for polyps or cancer inside the rectum and the entire colon. During the test, the doctor can find and remove most polyps and some cancers. Colonoscopy also is used as a follow-up test if anything unusual is found during one of the other screening tests. A colonoscopy is typically performed every 10 years (for people who do not have an increased risk of colorectal cancer). In addition, this would be the preferred test to evaluate for symptoms suggestive of colon cancer, like rectal bleeding.

CT colonography (virtual colonoscopy)

Computed tomography (CT) colonography, also called a virtual colonoscopy, uses X-rays and computers to produce images of the entire colon, which are displayed on a computer screen for the doctor to analyze. This procedure may be performed every five years. 


Treatments may differ depending upon the type of colorectal cancer diagnosed. 


Small rectal cancers that have not invaded the muscle of the rectum can sometimes be removed with surgery. Large rectal cancers may require radiation therapy and/or chemotherapy before surgery to minimize spread.

Surgery may be performed through an open (conventional) or minimally invasive or laparoscopic technique. Laparoscopic surgery can also be performed using a robot, which has arms controlled by the surgeon. This approach has been shown to result in reduced pain, a shorter hospital stay and faster recovery, compared to open surgery.

Radiation therapy

This therapy is recommended for cancer that has penetrated the wall of the rectum or involves surrounding structures or lymph nodes. Radiation is the transmission of high-energy rays that kill cancer cells in the vicinity of the rectum prior to surgery, which improves the chances the cancer will not return in the future.


Chemotherapy involves the use of drugs to kill cancer cells and stop replication. In rectal cancer, chemotherapy may be combined with radiation or prescribed alone. This treatment may take three to six months.

Watch and wait

In some rectal cancer patients, the cancer goes into remission after initial radiation and chemotherapy treatments. These patients may be placed under “active surveillance,” meaning they will have follow-up examinations to investigate return of the cancer. This approach may allow patients to avoid surgery and preserve the rectum.


Images of the rectal cancer are obtained before starting any treatment to determine the spread of the cancer. Imaging is also used to assess the effect that chemotherapy and radiation therapy have on a cancer during the course of treatment and prior to surgery.

Fertility treatment

Rectal cancer is increasing among young adults. Treatment for colorectal cancer can affect fertility in men and women. Younger patients may have a consultation with a fertility specialist to determine the best way to preserve their fertility.

American Cancer Society
National Cancer Institute
UT Southwestern Medical Center
Centers for Disease Control and Prevention

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